The mechanism of control of prostagandin synthesis is being investigated at a cellular level, with particular reference to the effect of Angiotensin II and hypersmolar sodium concentrations and to the role of intracellular calcium and sodium. The release of prostaglandin metabolites from the kidney into urine and renal venous blood will be measured, and evaluated as an index of renal synthesis of prostaglandins in vivo. The analytical approach will be stable isotope dilution, employing the multiple ion detector of the mass spectrometer. In addition, the application of stable isotope methods for PGD2 and 13,14-dihydro PGE2 to urine and renal venous plasma will be investigated. Factors governing renal prostaglandin synthesis in man will be investigated, and the possible role of prostaglandins in renal function with renal artery stenosis and during sodium deprivation will be studied.